All normal except for some micro boiling when DHW is demanded.
After the DHW has been running for a while, the gas valves suddenly shut down, the thermoelectric valve shuts down and the pilot goes out.
The boiler temp is not high enough to trip the boiler temp limit stat. at the point of...
Not the fan speed, not the venturi blocked or partially blocked. It turned out to be a small crack at the base of one of the plastic nipples on the underside of the presure switch (the nipple that plugs into the shorter pressure sampling tube in the flue). Only found it by accident! Bit of...
a switch that is said to be 'hunting' means that the physical switch contacts do not make a proper contact. Instead they pulse of fluctuate continually.